The present invention is generally directed to systems and processes for treating biological tissue, and particularly retinal tissue. More particularly, the present invention is directed to a process for heat treating retinal or other biological tissue using radiation, such as light beams, which create a therapeutic effect to a target tissue without destroying or permanently damaging the target tissue.
Retinal photocoagulation is a commonly used procedure for treating retinal diseases, including diabetic retinopathy. Retinal photocoagulation involves the use of light to create thermal burns in the retinal tissue. These thermal burns are believed to seal the retina and stop blood vessels from growing and leaking. Typically, the retinal laser burns are full-thickness in the areas of retinal pathology and visible at the time of treatment as white or gray retinal lesions. With time, these lesions develop into focal areas of chorioretinal scarring and progressive atrophy.
There are different exposure thresholds for retinal lesions that are haemorrhagic, ophthalmoscopically apparent, or angiographically demonstrable. A “threshold” lesion is one that is barely visible ophthalmoscopically at treatment time. A “subthreshold” lesion is one that is not visible at treatment time, but is detectable ophthalmoscopically or angiographically. “Suprathreshold” laser therapy is retinal photocoagulation performed to readily visible end point. In all cases, however, it is believed that actual tissue damage and scarring are necessary in order to create the benefits of the procedure. Photocoagulation has been found to be an effective means of producing retinal scars and has become the technical standard for macular photocoagulation for diabetic macular edema and other retinal diseases for many years.
Although providing a clear advantage compared to no treatment, current retinal photocoagulation treatments, which create retinal burns and scarring, have disadvantages and drawbacks. Conventional photocoagulation is often painful. This may require local anesthesia, which has its own attendant risks, or alternatively, treatment may be divided into stages over an extended period of time to minimize treatment pain and post-operative inflammation. Moreover, transient reduction in visual acuity is common following conventional photocoagulation.
In fact, thermal tissue damage may be the sole source of many potential complications of conventional photocoagulation which may lead to immediate and late visual loss. Such complications include sub-retinal fibrosis, choroidal neovascularization, and progressive expansion of laser scars. Inflammation resulting from the tissue destruction may cause or exacerbate macular edema, induced precipitous contraction of fibrovascular proliferation with retinal detachment and vitreous hemorrhage, and cause uveitis, serous choroidal detachment, angle closure or hypotony. While some of these complications are rare, others, including treatment pain, progressive scar expansion, visual field loss, decreased night vision, etc. are so common so as to be accepted as inevitable side effects of conventional laser retinal photocoagulation. Due to the inherent retinal damage in conventional photocoagulation treatment, treatment of the fovea and other sensitive areas of the retina is strictly forbidden, notwithstanding the most visually disabling diabetic macular edema occurs in these areas.
Another problem is that the treatment requires the application of a large number of laser doses to the area of the retina to be treated. This can be tedious and time-consuming as it is not uncommon for hundreds or even in excess of one thousand laser spots to be necessary in order to provide a full treatment. The physician is responsible for ensuring that each laser beam spot is properly positioned away from sensitive areas of the eye, such as the fovea, that could result in permanent damage. Point-by-point treatment of a large number of locations, using a single laser beam sequentially, tends to be a lengthy procedure, which frequently results in physician fatigue and patient discomfort.
The inventors have discovered that radiation, such as in the form of various wavelengths of light, can be applied to retinal tissue in a manner that does not destroy or permanently damage the retinal tissue, but achieves the beneficial effects on the eye diseases. The inventors have found that one or more light beams can be generated and applied to the retinal tissue such that it is therapeutic, yet sublethal to the retinal tissue, and avoids damaging photocoagulation in the retinal tissue, yet provides preventative and protective treatment of the retinal tissue of the eye. It is believed that the process raises the tissue temperature such in a controlled manner to selectively stimulate heat shock protein activation and/or production and facilitation of protein repair, which serves as a mechanism for therapeutically treating the tissue. It is believed that these activated heat shock proteins may reset the diseased retina to its healthy condition by removing and repairing damaged proteins. This then results in improved RPE function, improves retinal function and autoregulation, restorative acute inflammation, reduced chronic inflammation, and systematic immunodulation. The effects of the present invention may slow, stop or even reverse retinal diseases and improve visual function and reduce the risk of visual loss. It is believed that raising tissue temperature in such a controlled manner to selectively stimulate heat shock protein activation without damaging or destroying the tissue has benefits in other tissues as well.